Video from the LRV - where to find?

[Allan F]

Wouldn't it just be a case of designing the floor pan of the rover so it could protect a patch of soil? If the electronics and battery were placed on the centerline, and the rover stopped shortly after sunrise, there would be shadow under it. And if reflective covers were on the electronics/batteries, it would have same effect as a shelter.

[cjameshuff]

Wouldn't it just be a case of designing the floor pan of the rover so it could protect a patch of soil? If the electronics and battery were placed on the centerline, and the rover stopped shortly after sunrise, there would be shadow under it. And if reflective covers were on the electronics/batteries, it would have same effect as a shelter.

This might work for a large vehicle. The smaller the vehicle, the more light and heat is going to scatter in from the sides and conduct in from the edges and through the vehicle itself. I would be surprised if it worked for something people would call a rover.

Rather than a shelter, you might just carry a large sun-tracking solar array that keeps the rover and nearby ground in shade. Semi-permanent shelters just seem like decent places to stash equipment, samples, etc, and a simple half-cylinder "hog shelter" might be easy to supply multiples of in a light, compact package...little more than mylar and springy wire supports.

[Noldi400]

At local noon, the problem isn't sunlight so much as thermal radiation from the lunar surface, which hits over 100C. I like cjameshuff's idea of taking a siesta under some reflective blankets, but it would still need some sort of radiator to avoid reaching equilibrium temperature with the surface.

Don't forget that you're also going to need some means of dealing with dust; if the vehicle stirs up much dust at all, there's the camera lens(es), radiators, solar panels to think about. Not to mention anything that can't tolerate added insulation.

[Allan F]

At local noon, the problem isn't sunlight so much as thermal radiation from the lunar surface, which hits over 100C. I like cjameshuff's idea of taking a siesta under some reflective blankets, but it would still need some sort of radiator to avoid reaching equilibrium temperature with the surface.

Don't forget that you're also going to need some means of dealing with dust; if the vehicle stirs up much dust at all, there's the camera lens(es), radiators, solar panels to think about. Not to mention anything that can't tolerate added insulation.

Cameras could be equipped with the same system that Formula One racecar cameras have - an extra pane of glass in front of the lens. When it gets dirty, it rotates past a brush, cleaning it. Probably limited lifespan if regular glass, but a piece of sapphire should be scratch-resistant enough to provide useful lifespan.

Amount of dust would be speed-dependent. Just go slow enough, and dust from the vehicle itself will be very limited. How about static charge? What's the charge on the dust? Could a solar array be made to carry a static charge which would repel dust?


Edit: With a couple of square meters of solar cells, there could be something like 2000 watts availabe. That should be enough to run cameras, mobility and datalinks and still have enough to put into batteries. At night, the batteries would freeze, which wouldn't be good for capacity. But if they're isolated, they could be heated by a small heating element. It wouldn't require much. Electronics - how temperature tolerant could they be made?

[Chew]

Is solar power required for this hypothetical rover? Why not RTGs?

[cjameshuff]

Don't forget that you're also going to need some means of dealing with dust; if the vehicle stirs up much dust at all, there's the camera lens(es), radiators, solar panels to think about. Not to mention anything that can't tolerate added insulation.

It is a significant problem. IIRC, the LRV had issues with the battery compartment overheating specifically due to dust buildup.

Legged robots might have some advantages, possibly kicking up less dust to begin with and having joints that can easily be sealed.

[Allan F]

Is solar power required for this hypothetical rover? Why not RTGs?

Extended independent operation would be easier with solar power. Also, solar panels would be easier to lift from Earth than radioactive thermoelectrical generators. About one kilogram/square meter plus support structure. Voyager 1 has 3 plutonium-238 powered generators, and provide less than 500 watts of power with a weight of 120 kilograms. The rover would need additional chassis strength to carry enough RTG's to matter.

Unless you're talking about decades of independent operation. Then RTG's would be necessary, because of the degradation of the photovoltaic cells over time.

Edit: I don't know about the radiation from the RTG's and how it would affect electronics.

[Allan F]

Also, thermal control could be achieved by using the terrain for cover. You know about House Rock, right? There's shaded areas which would remain cool the entire lunar morning. At lunar noon, shade is probably difficult to find. But it's only for a few days (earth). After noon, drive to the other side, where there's shade. And at lunar night, there's a nice corner with radiant heating on two sides.

That leaves morning and afternoon to explore, when the sun isn't at full strength.

[ka9q]

Yes, that should work as long as the top surface of the blanket isn't exposed to much of the hot lunar terrain around it. Then it could use a high emissivity to radiate to the dark sky without also picking up much from the surface. (Sunlight can be rejected with low absorptivity.) I understand some of the ALSEP experiments at the Apollo 15 site had thermal problems because of longwave radiation from the surrounding mountains hitting their radiators.

[ka9q]

Extended independent operation would be easier with solar power.

I think some form of nuclear power will be essential on the moon for the forseeable future, to keep warm at night if not to generate sufficient electricity to keep operating.

Just about every active American experiment placed on the surface of the moon or Mars had at least some Pu-238, to my knowledge. Even the EALSEP seismometer deployed by the Apollo 11 crew had some small radioisotope heaters to stay warm at night though electrical power came from solar arrays. So did the Mars rovers Spirit and Opportunity. The two Viking landers and Curiosity are fully nuclear powered, of course. I'm not sure about Pathfinder and Phoenix.

The lunar soil has extremely low heat conductivity, so in the future it should be possible to dig caves on the moon that will have a fairly uniform temperature all day long, and it would be possible to go there to stay warm at night and perhaps around noontime.

[ka9q]

I don't know about the radiation from the RTG's and how it would affect electronics.

There's essentially no effect. That's why Pu-238 was chosen for RTGs. It's a pure alpha emitter, and nearly all of its decay products are also alpha emitters plus a few beta emitters; there are no hard gamma emitters that would be hard to shield. Radon is one of its daughters, so the material has to be enclosed if it's to be around humans, but that's about it.

RTGs are usually mounted on booms not so much to get the nuclear radiation away from the electronics and instruments, but to allow their waste heat to radiate to space.

Pu-238 also has a reasonable half-life, enough for a pretty long mission but not so long that its specific power (W/kg) would be unreasonably low.

[cjameshuff]

The lunar soil has extremely low heat conductivity, so in the future it should be possible to dig caves on the moon that will have a fairly uniform temperature all day long, and it would be possible to go there to stay warm at night and perhaps around noontime.

This was essentially what was behind my hog shelter idea. Limit direct heating by sunlight and loss of heat at night, for a temperature range that stays closer to something a bit under the surface, except without having to actually dig a burrow.

[ka9q]

You're probably right, though to be sure we'd have to do a full-blown analysis. You'd take all the surface properties and integrate the volume around them for the effects of dark sky, sun and lunar surface.

I guess I was thinking of underground shelters because they'd eventually be needed for a manned base to wait out solar particle events.

[Allan F]

I hope I'm not considered off-topic with all this.

It is fascinating to speculate about the possibilities. I suppose the navigation and communication would be integrated into one system. Maybe a backup-system like the original LRV's gyroscopic pointer, but primary navigation using a digital computer and radio beacons like those used to guide aircraft to runways in bad weather.

How about lithium-based batteries? Would this be the best choice for a LRV?

[ka9q]

The original navigation system on the LRV left a lot to be desired. Not that it could have been made much better at the time. The moon still lacks a magnetic field or a GPS.

The astronauts didn't really need it either, as they could just follow their own tracks back to the LM if they couldn't see it.

It's usually worth trying to piggyback navigation onto communications. High speed digital communications is often well suited to navigation, especially direct sequence spread-spectrum modulation. GPS and a lot of mobile phones have used it, though communications is now moving away from spread spectrum toward OFDM, which doesn't provide the highly accurate propagation delay measurements you need for navigation.

Optical ranging is another possibility between nodes within line of sight as the moon has no atmosphere to interfere.